Integrated-optic waveguides normally consist of a layer of lower cladding deposited upon a substrate, a layer of a core material deposited upon the layer of cladding, and another layer of cladding deposited on top of the core. The two layers of cladding need not be of the same material. Indeed, the top layer is sometimes air. Also, the lower cladding may be the substrate. The index of refraction, n.sub.core, for the core must be significantly greater than the index of refraction for both claddings. This difference causes the peak intensity of the optical mode to be contained in the core while the "tails" of the mode extend into the cladding.
The complex index of refraction for a material may be written as follows: EQU n=n+ik
where k is the absorption variable, which, as shown above, is the imaginary part of the complex refractive index. In most cladding materials, it is desired that the k be very small, so the refractive index approximately equals n. The effective index for a guided mode is a function of both the core and cladding indices since the mode extends into the claddings, and is thus also complex-valued.
Metals, which can be used as a cladding, possess a relatively large value for k. This larger value results in more of the light being absorbed than with a dielectric cladding, making a metal-clad waveguide very lossy. The amount of loss in the waveguide is a function if interaction length of the metal, the proximity of metal to the core, and the direction of polarization of the mode. This apparently undesirable property can make metal in optical waveguides very useful. It is possible to effectively change the imaginary part, k.sub.eff, of the effective index of the guided mode by bringing metal into close range or contact with the core, the metal acting like a switch or attenuator. Additionally, metal can be used to alter the real part of the effective index, n.sub.eff, to create devices such as directional coupler switches, switchable Bragg deflectors, and the like.
Using the processing techniques developed in deformable mirror device (DMD) technology, it is possible to form a waveguide with a metal membrane supported upon the upper cladding. The membrane can be controlled to bring it into proximity with the core to alter the effective index of the guided mode.